Consider the question. Boston Celtics center Bill Russell holds the record for the most NBA championships won with 11 titles during his 13-year playing career. He won his first championship with the Boston Celtics in his rookie year. Afterwards, he went on to win ten championships in the next 12 years, including eight consecutive championships from 1959 to 1966. He won the last two championships in 1968 and 1969 as player-coach. Russell's teammate, Sam Jones, won ten championships from 1959 to 1969, the second most in NBA history. Four Celtics players, Tom Heinsohn, K.C. Jones, Satch Sanders and John Havlicek, won eight championships each. Two other Celtics, Jim Loscutoff and Frank Ramsey, won seven championships each. Four players, Bob Cousy, Kareem Abdul-Jabbar, Michael Jordan and Scottie Pippen, won six championships each. Jordan and Pippen are members of the Chicago Bulls team who won three consecutive championships twice in the 1990s. George Mikan won two championships in the NBL before it merged with the BAA to form the NBA, and won five championships in the NBA.

Answer this question based on the passage: who has the most nba championships in nba history?
 What is the step-by-step reasoning process to arrive at the answer: Boston Celtics center Bill Russell?
The important part for answering this question is: Boston Celtics center Bill Russell holds the record for the most NBA championships won with 11 titles during his 13-year playing career.